1. Field of the Invention
The present invention relates to a gear pump or motor of a circumscribing type usable in a field of hydraulic apparatus or the like.
2. Description of the Related Art
A gear pump or motor of this kind is provided with a pair of gears brought in mesh with each other, shafts respectively extended from front and rear sides in axis center directions of the gears, and a pump main body containing these, for making a hydraulic fluid (oil) flow from a high pressure region of a meshed portion to a low pressure region of other meshed portion by rotating the two gears. According to the gear pump or motor, the pump main body is constituted by a front shaft containing main body for containing the shafts on a front side, a gear containing main body for containing the gears and a rear shaft containing main body for containing the shafts on a rear side.
There are three kinds of types of combining constituent elements of the pump main body as follows. A first type is a type of coupling the front shaft containing main body, the gear containing main body and the rear shaft containing main body to each other respectively as separate members, a second type is a type of integrating the front shaft containing main body and the gear containing main body, and a third type is a type of integrating the gear containing main body and the rear shaft containing main body. A pump main body integrated with the gear containing main body and the rear shaft containing main body is referred to as a ‘gear•rear shaft containing main body’ as follows and the type achieves advantages of reducing a number of parts in comparison with a constitution separately constituting the respective main bodies, facilitating to install a comparatively large suction port (low pressure) or delivery port (high pressure) at a side face of the main body and is reduced to practice (refer to, for example, JP-A-08-121351).
The gear•rear shaft containing main body is constituted by a bottomed shape and the bottom is installed with a bearing hole and it is necessary that high pressure is not generated at the depth portion. For that purpose, the depth portion of the bearing hole is communicated with the low pressure region (for example, suction port) Specifically, there is carried out a measure or the like of forming communicating means for communicating a face of the rear shaft containing main body brought into contact with the depth portion, that is, a region at a rear face of the rear shaft containing main body to the low pressure region and forming a communicating path for communicating bearing portions of the two gears to the low pressure region.
For example, according to a type of forming a low pressure communicating path by boring an inclined hole from a side of the gear containing main body and boring a hole for communicating to low pressure at an inner peripheral face of the bearing portion by recessing, a surrounding of the bearing hole is subjected to countersinking in an elliptical shape, the bearing is integrated by constituting a projected height slightly lower than a depth of the countersinking and a seal member is caught by an outer side thereof. Further, a hole communicating with a low pressure portion is bored at an inner portion subjected to the countersinking and a spacer for hampering deformation of the seal member by a negative pressure is inserted thereto. Further, when the pump main body is fabricated by a die cast system, there is carried out a method of previously forming a groove at a portion of the main body and connecting the groove to the low pressure communicating path.
However, according to the method of forming the low pressure communicating path by the inclined hole, a long slender hole needs to bore, time is taken for the working, further, a hole bored on the side of the pump main body must be closed. Further, recessing requires time and labor in working. Also the method of previously forming a die requires a working time period and a problem is posed in working accuracy. Further, according to the method of forming the low pressure communicating path by the inclined hole, the long slender hole needs to bore, time is taken in the working, further, the hole bored on the side of the pump main body needs to close. Further, also recessing is operation taking time in working and requiring labor. Also the method of previously forming the die at the cast product poses a problem that a working time period is required and working accuracy is low. Further, a consideration is taken in the projected height in integrating the bearing, the portion does not function as the bearing and therefore, an extra bearing length is needed and a cost is increased.